std::ranges::data
<ranges>
<iterator>
inline constexpr /* unspecified */ data = /* unspecified */;
(customization point object)
requires /* see below */
constexpr std::remove_reference_t <
Returns a pointer to the first element of a contiguous range.
If T is an array type and std::remove_all_extents_t <std::remove_reference_t <T>> is incomplete, then the call to ranges::data is ill-formed, no diagnostic required.
If the argument is an lvalue or ranges::enable_borrowed_range <std::remove_cv_t <T>> is true, a call to ranges::data is expression-equivalent to:
- decay-copy (t.data())(until C++23)auto(t.data())(since C++23), if that expression is valid and its type is a pointer to an object type.
- Otherwise, std::to_address (ranges::begin (t)), if the expression ranges::begin (t) is valid and its type models std::contiguous_iterator .
In all other cases, a call to ranges::data is ill-formed, which can result in substitution failure when ranges::data(e) appears in the immediate context of a template instantiation.
Customization point objects
The name ranges::data denotes a customization point object, which is a const function object of a literal semiregular class type. See CustomizationPointObject for details.
[edit] Notes
If the argument is an rvalue (i.e. T is an object type) and ranges::enable_borrowed_range <std::remove_cv_t <T>> is false, the call to ranges::data is ill-formed, which also results in substitution failure.
If ranges::data(e) is valid for an expression e, then it returns a pointer to an object.
The C++20 standard requires that if the underlying data function call returns a prvalue, the return value is move-constructed from the materialized temporary object. All implementations directly return the prvalue instead. The requirement is corrected by the post-C++20 proposal P0849R8 to match the implementations.
[edit] Example
#include <cstring> #include <iostream> #include <ranges> #include <string> int main() { std::string s{"Hello world!\n"}; char a[20]; // storage for a C-style string std::strcpy (a, std::ranges::data(s)); // [data(s), data(s) + size(s)] is guaranteed to be an NTBS std::cout << a; }
Output:
Hello world!
[edit] See also
(customization point object)[edit]